Typeclass with multiple parameters issue

typeclass-issue.scala

trait Feedtype
trait Atom extends Feedtype
trait Rss2 extends Feedtype
case object Atom extends Atom
case object Rss2 extends Rss2

trait Encoding
trait Xml extends Encoding
trait Json
case object Json extends Json
case object Xml extends Xml

trait Content
case class show[T <: Feedtype,E <: Encoding](str: String, tp: T, en: E) extends Content

trait TypeClass[C,D,E] {
  def show(c: C, d: D, e:E): String
}

trait Service{
  def print[T,C,D](t: T,c:C, d:D)(implicit s: TypeClass[T,C,D]): String
}

object Service extends Service{
  def print[T,C,D](t:T, c:C, d:D)(implicit s: TypeClass[T,C,D]): String =
    s.show(t,c,d)
}

implicit val t1 = new TypeClass[show[Atom,Xml], Atom, Xml] {
  def show(c: show[Atom,Xml], d:Atom, e:Xml) = c.str
}

implicit val t2 = new TypeClass[show[Rss2,Xml], Rss2, Xml] {
  def show(c: show[Rss2,Xml], d:Rss2, e:Xml) = "hi there " + c.str
}

val s1 = show("some show", Atom, new Xml {})

Service.print(s1, s1.tp, s1.en)

Current error after making the case class show polymorphic on types is this

type mismatch;
 found   : A$A10.this.typeclass[A$A10.this.show[A$A10.this.atom,A$A10.this.xml],A$A10.this.atom,A$A10.this.xml]
 required: A$A10.this.typeclass[A$A10.this.show[A$A10.this.atom.type,A$A10.this.xml.type],A$A10.this.atom.type,A$A10.this.xml.type]
service.print(s1, s1.tp, s1.en)(t1);}
                                ^

figured out that issue is that atom and xml being case objects when they are being used as values to create s1. If I use new atom {} or new xml {} then the execution is happening fine. However, I wonder why are the case objects being considered a different type than the types that they represent ?

Got a superb reply to this issue to my StackOverflow post here
http://stackoverflow.com/questions/39559806/scala-typeclass-with-multiple-parameters-error